1978 full size Bronco with a 1st gen 12v

[American Thunder]

Originally Posted by farmfuel

Those look like 9" skyjacker coils. I'm supprised to see that you don't have an adjustable track bar and drag link. Isn't your 44 hanging out on the driver's side fender? Mine did.

I wouldn't sweat the strength of those 9" axle shafts- they're solid. compare them to a 12 bolt, and you'll be glad you have a 9". The 335 series motor probably doesn't weigh much less than your 12V motor. I put a 91 12 valve on my scale up here at work- 980lbs.
My guess is that your old 351M/400M weighs maybe 700+ lbs?

The skyjacker suspension was already installed when I bought the truck, I did find the receipt for all the parts, maybe I can look up the numbers and confirm if the lift is 6", as the previous owner said it was. (the Bronc is pretty damn tall, though) It still has a '92 inspection sticker on the windshield, and that brand new suspension has only sat in a garage the last 16 or 17 years. (The Receipt of the parts I found has a date of '92 or '93 on it, and the grand total was almost $1000)
As for the trac bar, I fabricated a 4" extension for the factory mount that drops it down, so that the stock trac bar now runs parallel with the drag link. (in other words, NO bump steer.. I hope) I did have to use a strap to pull the frame over 1/2" or so so I could get the bolt in, but nothing you can see by sighting down the sides of the truck.
You're right about the weights of the motors. A finished big fat 460 motor weighs 750 or so, the 400 isn't much less. What I'm doing that most people don't mention in swaps is moving the Cummins back as far as I possibly can, in order to move not only the weight of the motor back some, but also the weight of the C6 trans and that massive NP205 iron case, too. Even moving the drivetrain back only 3 or 4 inches means a huge reduction in nose weight. I'm buying a glass hood for it at some point, so all together, the nose of the Bronc should be fairly close to the nose weight of what it was with the stock motor. The added benefit, of course, being more weight on the back end, meaning better traction and handling.
I think the D44 up front will survive just fine, unless I try some stunt like a 4wd burnout on pavement or something.
I'm not sure about the 9" 31 spline axles, but yes, you are correct about the strength of the 9" parts, it has a legendary reputation for reason. If an axle does break, my next plan will be a 35 spline detroit locker with 3.00 gears and 35 spline aftermarket axles. Also must keep in mind when determining axle durability that with a higher gear ratio like the stock 3.50s, there is less stress on the axles and more on the rest of the drive line than you'd have with deeper gearing, such as the typical 4.10s or 4.56s. Also, the fact that the Bronco is so much lighter than the usual Cummins powered truck.

Stress = torque x mass!!

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1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

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Last edited by American Thunder : 08-21-2009 at 08:38 PM.

[farmfuel]

What I would be concerned about is the lift- my bronco has 9" coils up front, and 6" springs in the rear. Both driveshaft angles are horrible. The only solution is to lower the tranfer case, which you've probably eyeballed, is near to impossible to do with regard to the radius arm drop brackets installed. I've thrown an overhauled rear shaft before, just running 40mph down the road. Those 1310 U-joints mixed into that CV at the fixed yoke on the 205 spells disaster (due to the angle). I had my shaft legthened 2" to compensate for the lift. You will find that a F250 with a 205 runs a larger rear Yoke, and I think takes a 1330 U-joint. The rear output yoke is bigger on a F250 for sure. It may be worth checking into. I have that 3/4 ton 205 yoke if you need it.

Also something else you may want to check into is the clearance issue you will have with the oil pan and the engine crossmember...have you investagated this, and what is your take on it? The motor being further back may aliveate this problem? It's worth checking into.

The 9" coil will help, due to the wire diameter that it has. It's meant for ride height, not flex, so a shorter lift coil won't have a wire diameter as thick.

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93 D250, 2WD, 5 speed ext cab
89 F350, 4WD W/ Banks sidewinder, 5 speed, Reg cab SRW
78 Bronco w/ 435 & 205, chopped top- no doors...summertime buggy.

[farmfuel]

I did the same thing you did with taking two shock towers and cutting one down and welding it to the other- in an effort to correct the track bar...it still wasn't enough; I had to buy a Superlift adjustable track-bar. Once I was over that hurdle, I noticed that it didn't turn to the right for $hit, and ended up having to buy an adjustable drag link to compensate for the poor steering to the right.

FYI- 4BT motors were seen in front of NP435's- I'm not sure if it's the small block bellhousing bolt pattern or not. Good luck finding one, but if you did, you could put a NP435 beinnd your 6BT...and it would bolt right up to the Cummins adapter plate. (all OE equipment)

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93 D250, 2WD, 5 speed ext cab
89 F350, 4WD W/ Banks sidewinder, 5 speed, Reg cab SRW
78 Bronco w/ 435 & 205, chopped top- no doors...summertime buggy.

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Last edited by farmfuel : 08-22-2009 at 10:45 AM.

[American Thunder]

That front crossmember you mention, the nice, smooth curved one, (which I really don't want to cut and modify) will clear the front of the oil pan by 3/8" if I've measured correctly. That's a big reason I wanted the motor back as far as possible. The other benefit of moving the whole drivetrain back 3" is that the stock rear shaft should work nicely, considering the lift.
The '78 firewall looks like it's made for an inline 6 Cummins, because of that huge indentation it has.

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1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

[American Thunder]

Originally Posted by farmfuel

FYI- 4BT motors were seen in front of NP435's- I'm not sure if it's the small block bellhousing bolt pattern or not. Good luck finding one, but if you did, you could put a NP435 beinnd your 6BT...and it would bolt right up to the Cummins adapter plate. (all OE equipment)

Hmm.. not an option for me, I want acceleration, so the auto is the only way to go. Shifting a blocky 4-speed like the 435 would slow me down! Can't let that turbo pressure escape in between shifts, afterall. heh

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1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

[American Thunder]

My Bronco will be painted in a Measure 32D Iowa-class battleship camo scheme from 1942, sort of a battleship theme throughout. I'm even calling it by a battleship hull designation of "BB-78", which in this case means "Big Bronco '78", of course.

This paint scheme.


And these custom decals on the rear window.

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1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

[American Thunder]

The motor is sitting on its mounts in my Bronco as of 3 hours ago. It took awhile to sneak it into place with the radiator support still bolted in the truck, but I didn't break anything. Thank God I had the fork lift that can pick the engine up high enough. It actually only cleared the support by a couple inches at max height, because the truck is so tall.
That a/c bracket down at the bottom has to go, however, it's in the way of the crossmember. I was hoping I could use the factory dodge a/c compressor at some point on the truck, but it definitely can't mount in the stock location. Otherwise, the front crossmember won't need to be cut or anything, it's a great fit. Even the stock dodge 3" downpipe fits like it was made for the truck.(clears the firewall by 2") Without the 3" body lift, I would have big time issues with the clearance at the transmission adapter, because the 12v sits right inside the firewall indentation, but as it is, it fits like the Bronco was made for it. The front of the oil pan clears the crossmember by 1/4" - 1/2", and the harmonic balancer misses the crossmember by less than that. I forgot to bring my dig. camera earlier, but I'll get some pics tomorrow and post them.
And the front of the truck didn't drop as much as I thought it would. I figured on maybe 2.5", but it only dropped maybe 1 or 1.5 inches at most. Likely due to the fact that the engine is sitting so far back. I'm loving the way the Cummins looks in there!

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1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

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Last edited by American Thunder : 08-22-2009 at 11:18 PM.

[American Thunder]

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1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

[tyler886]

Wish I had that much firewall space to work with in my Bronco when a Cummins goes in!

I'll be following this build!

-Tyler

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Still doing homework on my 1-Ton Cummins powered Bronco

[American Thunder]

The 3" of body lift is a huge help. But that indentation in the firewall fits around the Cummins like a glove.

__________________
1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

[American Thunder]

I discovered today that the exact spot the engine mount needs to go is 1 1/8" rearward of the middle factory bolt hole in the framerail. So I figured I'd drill a new hole there, and just drop a bolt through. The only problem was, a bolt for the spring perch and its reinforcing piece was directly underneath, so wasn't room to drill and bolt it there.
I decided to make a couple of steel plates from 1/2" stock that would bolt to each frame rail, using 2 of the original integral nuts and all.

Front side.

Back side.
I countersunk the two 1/2" holes, so the bolt heads would be flush. I also drilled a 5/8" countersunk hole, turned down the head of a 5/8" bolt, dropped the bolt in the hole, welded it in place, and then ground it smooth, creating an integral stud that the engine mount will fit over.

Here's the finished(unpainted) piece with the mount insulator in place.


Finished, painted, installed. Note the flush mount 1/2" attaching bolts.


The other side, identical.

The motor sits just where I want it to, and I'm happy with the way these plates turned out.

__________________
1978 Bronco - 1991 12V, Dynamic C6 Ford auto with billet torque converter, NP205 case, 3.50:1 lockers. 9" lift, 35" tires, 366 spring, pump mods. - Still under construction.

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Last edited by American Thunder : 08-31-2009 at 12:51 AM.

[chrapladm]

Nice build!!

Being a nube its nice to see all these detailed pictures so I can see what everyone is talking about. I know alittle bit about broncos and F100's but to see such detailed pics its nice to jog the memory and learn better ways of doing things.